They say his planned 85,000-square-foot family compound pushes the bounds of common sense and decency.

Reporting from Los Angeles and London — Nobody in wealthy Benedict Canyon can say for sure what his name is or where he's from, but the owner of a pricey 5.2-acre property on Tower Lane is fast becoming persona non grata among an exclusive club of Los Angeles homeowners.

In a neighborhood whose residents include Bruce Springsteen, Jay Leno, Michael Ovitz and David Beckham, this mystery landowner is preparing to build an 85,000-square-foot family compound, fit for royalty.

The proposed complex is an eclectic mix of European architecture in the coveted 90210 ZIP Code. Although the area teems with mansions boasting swimming pools and tennis courts, residents say the scale of this "megamansion" pushes the bounds of common sense and decency.

If the owner gets his way, the real estate will host a 42,681-square-foot main house, a double-winged "son's villa" of more than 27,000 square feet, a 4,400-square-foot guest house, a 5,300-square-foot staff quarters and a 2,700-square-foot gatehouse. Those and other proposed structures would occupy a combined area larger than Griffith Observatory.

"It's commercial-scale construction, like building a Wal-Mart in the heart of a quiet residential neighborhood," said Martha Karsh, who lives with her husband, Bruce, just east of the site.

In an area known more for gated estates than block parties, the controversy has so far united more than 150 residents. Through e-mails, house gatherings and phone calls, opponents have built support for their cause. Next, they plan to mount a door-to-door campaign and launch a website.

They seem to have a worthy adversary, one with deep pockets and expensive lawyers and who may even be a senior Saudi prince. Instead of disclosing his identity, the owner has created a special business, Tower Lane Properties Inc., to purchase three adjoining plots for $12 million. A team of lawyers, architects, intermediaries and sales brokers have been hired to manage the project, and all have signed secrecy agreements.

"We're not trying to be deceptive," said attorney Marc E. Petas, a Tower Lane Properties representative in Los Angeles. "It's just a matter of maintaining privacy."

City planning documents list Mansour Fustok of London as the president of Tower Lane Properties, with Rutter Hobbs & Davidoff Inc., a Century City law firm, as the "in care of" contact.

Fustok, a former brother-in-law to Saudi King Abdullah, is uncle to Prince Abdulaziz ibn Abdullah ibn Abdulaziz al Saud, one of King Abdullah's sons. Rutter Hobbs attorney Olivia Goodkin, who served as the initial registered agent for Tower Lane Properties, has represented companies controlled by Saudi royal family members in the past.

A Tower Lane Properties representative told residents during a project presentation at one of their homes that the owner is a single father of three whose family would occupy the grounds only occasionally. Project opponents point out that Prince Abdulaziz is divorced and has three children.

Reached at his home in London, Fustok said he was prohibited from naming the owner and described the proposed development as "just a normal Mediterranean-style house." He insisted that the owner would comply with all building regulations and environmental reviews.

"All I'm trying to say is a very nice family is going to live over there," Fustok said. "It's a 5-acre lot altogether. It is far from everybody. … You buy a lot of land, you think you have the right to build on it.

"To face something like this, objecting to everything, it is too much," Fustok said. "Mrs. Karsh and Mr. Ovitz are the ones causing this mayhem and delaying things and so on."

Ovitz declined to be interviewed, but an associate who asked to remain anonymous described his position this way: "He just wants his neighbors to obey the law. It isn't personal or project-specific."

Residents of the canyons above Sunset Boulevard have defeated foreign royalty before. In the early 1990s, the sultan of Brunei proposed a 59,000-square-foot estate on Tower Road in Beverly Hills, near the Tower Lane site in Los Angeles. Sidney J. Sheinberg, a former entertainment industry executive, and the late actor Jack Lemmon were among those who complained loudly enough to quash the plan.

Ovitz himself sparked a neighborhood furor when he proposed a 28,000-square-foot megamansion on property straddling the Los Angeles-Beverly Hills border, but he fared better than the sultan after a battle that lasted several years. The former Hollywood agent-turned-investor's sleek, art-filled structure sits a stone's throw from the proposed Tower Lane development.

Royally owned or not, the site in dispute has had a colorful past.

The gates at the top of winding Tower Lane, a private road, open onto what must have seemed a remote wonderland in the late 1920s when movie director King Vidor hired Wallace Neff to design a 17-room, 8,010-square-foot Spanish Colonial hacienda.